(in the classification of related languages within a family) a category of a lower order than a subbranch and of a higher order than a subgroup:

the Low German group of West Germanic languages.

any grouping of languages, whether it is made on the basis of geography, genetic relationship, or something else.

5.

Geology. a division of stratified rocks comprising two or more formations.

6.

Military.

Army. a flexible administrative and tactical unit consisting of two or more battalions and a headquarters.

Air Force. an administrative and operational unit subordinate to a wing, usually composed of two or more squadrons.

7.

Music. a section of an orchestra comprising the instruments of the same class.

8.

Art. a number of figures or objects shown in an arrangement together.

9.

Mathematics. an algebraic system that is closed under an associative operation, as multiplication or addition, and in which there is an identity element that, on operating on another element, leaves the second element unchanged, and in which each element has corresponding to it a unique element that, on operating on the first, results in the identity element.

group

n.

1690s, originally an art criticism term, "assemblage of figures or objects in a painting or design," from French groupe "cluster, group" (17c.), from Italian gruppo "group, knot," perhaps ultimately from Proto-Germanic *kruppaz "round mass, lump," and related to crop. Extended to "any assemblage" by 1736. Meaning "pop music combo" is from 1958.

Two or more atoms that are bound together and act as a unit in a number of chemical compounds, such as a hydroxyl (OH) group.

In the Periodic Table, a vertical column that contains elements having the same number of electrons in the outermost shell of their atoms. Elements in the same group have similar chemical properties. See Periodic Table.

Mathematics A set with an operation whose domain is all ordered pairs of members of the set, such that the operation is binary (operates on two elements) and associative, the set contains the identity element of the operation, and each element of the set has an inverse element for the operation. The positive and negative integers and zero form a set that is a group under the operation of ordinary addition, since zero is the identity element of addition and the negative of each integer is its inverse. Groups are used extensively in quantum physics and chemistry to model phenomena involving symmetry and invariance.